1. Field of the Invention
The present invention relates to a battery pack.
2. Description of the Related Art
Generally, unlike a primary battery, a secondary battery is a battery capable of being charged and discharged for several times. The secondary battery manufactured in a shape of a battery pack has been widely used as a power supply for portable electronic devices, such as a cellular phone, a notebook computer, a camcorder, etc.
In particular, among secondary batteries, since a lithium ion secondary battery has a relatively high operational (or working) voltage and a relatively high energy density per part weight, the lithium ion secondary battery is more suitable for the field of portable electronic devices. Further, among lithium ion secondary batteries, since a lithium polymer battery using a polyelectrolyte has shape versatility and flexibility, it can be formed to be relative thin (or slim) to reduce the dimensions of the portable electronic devices.
A conventional battery pack includes a bare cell having an electrode assembly formed by winding a positive electrode plate and a negative electrode plate and a separator interposed between the positive electrode plate and the negative electrode plate, and an inner case in which the wound electrode assembly is sealed while exposing anode and cathode terminals of the electrode assembly. The battery pack is completed by sealing the outer surface of the bare cell with an outer case in a status that a safety device such as a protection circuit board is mounted on an outer surface of the bare cell.
When the battery pack is used as a power supply for portable electronic devices, it is more important to have relatively high structural stability and stiffness than to have relatively high efficiency of the bare cell. Further, the battery pack needs to be relatively slim (or thin) in order to slim and minimize the dimensions of the portable electronic devices. The key to slimming the battery pack is the structure of the outer case forming an exterior shape of the battery pack.
In particular, the thickness of each of the bare cell, protection circuit board and outer case has considerable influence on the slimming of the battery pack. As the capacity of the bare cell is higher, the thickness of the battery pack is increased. Therefore, it is the thickness of the outer case that should be reduced in order to slim the battery pack while maintaining or even increasing the capacity of the battery pack.
However, in the case of a conventional outer case formed with a resin material, it is difficult to have a thin thickness while maintaining the strength thereof. For example, it is difficult to reduce the thickness of each of the front and rear cases forming the outer case to be less than 0.4 mm.